ERA+ calculation modified

[HoustonGM]

http://www.baseball-reference.com/blog/archives/5159

Right now on the site you'll see different ERA+ numbers from what you are used to seeing on the site. The old formula was 100*(lgERA/playerERA). The numbers you see now are 100*(2- playerERA/lgERA). This changes the numbers somewhat and bunches the top end a bit more, but doesn't change the ranking of players. The two lists of league leaders are the exact same

Thanks in part to Tango:

I was on Sean’s case like crazy regarding ERA+, as many of you know. Basically, while every other index stat in the world did the value of the metric divided by the “average”, ERA+ did the league average divided by the ERA of the player. In effect, instead of ER per IP, it was doing IP per ER. What made it worse is when people started to use this in calculations, using it for simple averages etc. The math did not work out.

I had proposed that he do it the consistent way, which would mean someone who gives up runs at half the league average show as 50, rather than 200. Sean was rightfully concerned that people are used to “bigger is better”, and so, that would look like a sticker shock.

Guy proposed something very simple: 2 - ERA/lgERA then times 100. This way, what would look like 50 for me would show up as 150. And the top end is 200 in the Guy method (or 0 in my method). And Sean did just that.

Adjusting to the new scale will take some getting used to. Pedro Martinez's 166 in 2000 is now the all-time best single-season score (for a starter), rather than the 293 or whatever it used to be.

[filihok]

Yeah...I'm not sure I like the change, but it's probably just the old case of humans not liking change.

Yeah for Guy because a 150 ERA+ sure sounds better than a 50 ERA+ but, my early morning math skills aside, doesn't the "2 -" create some scaling problems since a 200 would become the max

[dps]

Yeah, I don't like the fact that there is now a top end boundary. Granted, it'll probably never come into play, but there's potential for a problem there.

[HoustonGM]

The new scale is set up to actually be what people always talked about ERA+ like. 100 is still exactly average. However, now, 120 = 20% better than average, 130 = 30% better than average, etc.

Tango in a BTF comment:

This is what the scale looks like then and now, presuming league average of 4.00 :

ERA old new
1.00 400 175
1.50 267 163
2.00 200 150
2.50 160 138

3.00 133 125
3.50 114 113
4.00 100 100
4.50 89 88
5.00 80 75

5.50 73 63
6.00 67 50
6.50 62 38
7.00 57 25

The point is that the guy with the 3.00 ERA is as far from 4.00 as the 5.00 ERA guy is from 4.00. They are both 1 run away. The new ERA+ scale shows that properly. The old one did not.

These pitchers are all 1 run apart from each other:

ERA old new
1.00 400 175
2.00 200 150
3.00 133 125
4.00 100 100
5.00 80 75
6.00 67 50
7.00 57 25


So, yeah, the old ERA+ would cause severe distortions. The 1.00 ERA guy is as far from 4.00 as the 7.00 is. The average of the two (1.00 and 7.00) is league average.

The new scale, with 175 and 25, gives you an average of 100 and they are symmetrical.

In the old scale, how is it apparent that 400 and 57 together average out to 100?

I think the new scale does make more mathmatical sense, it's just that now everyone has to readjust what they thought about the scale. I had grown used to the scale, where something like 190+ was a legendary season, 150/160 was the usual league leader, etc. Now, 166 is the all-time record, so it'll take some time to adjust to it and be able to eyeball it and know exactly what it means again.

[HoustonGM]

I agree with this:

The change makes sense, but I agree with those who say it should have been better publicized, and that the stat should have been given a new name. None of the old discussions, articles, etc. are going to make any sense now.

The publicized part isn't relevant as this discussion was taking place prior to Sean Forman making the blog post on B-R, but I agree that they should leave the old ERA+ stat up and put the new one up as well.

[Alloutwar]

::insert Mom's basement jokes here::

This is huge news. This is bigger than when a leak sprang overhead and I had to move out of mom's basement for 2 days.

ERA+ was modified? Holy crap. Shouldn't it be ERA++ now, in following nerd precedent?

Quick, somebody tell Joe Morgan, so he knows the new scale before his first game this season.

[kenny1234]

http://www.baseball-reference.com/blog/archives/5159

UPDATE: As I said above, it was not my intent to roll this out at this time. I still believe this to be a good idea, but it needs to be done in a MUCH more organized manner, so I'll be rolling back to the old stat tonight or tomorrow and then taking a more measured approach going forward. I apologize again for the confusion.

And just to add to the confusion, they have already backtracked and gone back to the old stat.

[gRYFYN1]

Yeah...I'm not sure I like the change, but it's probably just the old case of humans not liking change.

Yeah for Guy because a 150 ERA+ sure sounds better than a 50 ERA+ but, my early morning math skills aside, doesn't the "2 -" create some scaling problems since a 200 would become the max

I get why its done the way it is with "+" stats really being a percentage number. With ERA being a lower is better number you theoretically cant be more than 100% better than average, as that would be below 0.

The only "issue", I suppose (at the scaling thing), is that you could be more than 100% worse, and the new system zero's out after that - which is why the system really should just be reversed with lower is better system hinted at by tango.

[HoustonGM]

And just to add to the confusion, they have already backtracked and gone back to the old stat.

They didn't "back track" really. As Sean said, it came out early on accident.

[HoustonGM]

Another comment that closely matches my thoughts:

As logical as this change seems to be it appears that it will be more useful to the very small set of people who do various calculations than it will be to the majority of us who simply like it as a tool to figure out if someone had a good year. Now we have to adjust our mental scale.

[kenny1234]

They didn't "back track" really. As Sean said, it came out early on accident.

All I meant was that they went back to how it was before. I don't care how they define ERA+, so it really wasn't a comment that meant anything else.

[kenny1234]

Another comment that closely matches my thoughts:

And I would guess that most people that use it to make calculations were smart enough to adjust for the issues before anyway - so this is almost entirely irrelevant.

[HoustonGM]

All I meant was that they went back to how it was before. I don't care how they define ERA+, so it really wasn't a comment that meant anything else.

Ah

And I would guess that most people that use it to make calculations were smart enough to adjust for the issues before anyway - so this is almost entirely irrelevant.

Yeah.

I understand perfectly why the new calculation is "better", and it absolutely should be available. It just shouldn't replace the ERA+ everyone has come to know, though.